Rotation angle detector

ABSTRACT

A rotation angle detector for detecting a rotation angle of a detectable rotation body, comprises: a primary rotation body to be attached to the detectable rotation body and to rotate as integral with the detectable rotation body; a secondary rotation body to rotate as a predetermined rotation ratio for the primary rotation body; a primary rotation detection mechanism to output a signal to be varied periodically as corresponding to a rotation of the primary rotation body; a secondary rotation detection mechanism to output a signal to be varied periodically as corresponding to a rotation of the secondary rotation body; a signal processing unit to calculate the rotation angles of the primary and the secondary rotation bodies using the signals that the primary and the secondary rotation detection mechanisms output; and an operation processing unit to calculate the rotation angle of the detectable rotation body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a US national stage filing of Patent CooperationTreaty (PCT) Application Serial No PCT/JP2007/062048 (WO2007/149296),filed Jun. 14, 2007, which claims priority to Japanese PatentApplication No. 2006-164772, filed Jun. 14, 2006, and Japanese PatentApplication No. 2006-199663, filed Jul. 21, 2006, the entireties ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a rotation angle detector for detectinga rotation angle of a rotation body.

BACKGROUND ART

A conventional rotation angle detecting device as disclosed in a patentdocument 1 comprises a primary rotation body to rotate as integral witha rotation body and two of secondary rotation bodies to rotate ascoupled with such the primary rotation body. Moreover, the primaryrotation body and two of the secondary rotation bodies individuallycomprises a gear, wherein the number of teeth of the individual gearsare different from each other. Further, each of the gears of theindividual secondary rotation bodies and the gear of the primaryrotation body are meshed with each other respectively. Furthermore, eachof the secondary rotation bodies individually comprises a magnet and ananisotropic magnetoresistive (AMR) sensor to detect a magnetic field ofthe individual magnets. And then it calculates a rotation angle of therotation body, by using such as a phase difference between each ofdetection signals for the rotation angles of the individual secondaryrotation bodies that each of the AMR sensors outputs.

On the contrary, a conventional rotation angle detecting device asdisclosed in a patent document 2 comprises a rotating plate to berotated using a rotation body and a gear to be rotated with the numberof rotation as larger than that of the rotating plate by using therotation body or the rotating plate. Moreover, there is provided anencoder of absolute signal type at the rotating plate, and then a codesignal is output as a rotation angle detection signal for the rotatingplate, which is determined as one cycle for one rotation of the rotatingplate by such the encoder. Further, there is provided a magnetic sensorthat a magnet and a magnetoresistive element are used therefor at thegear, and then an analog signal is output as a rotation angle detectionsignal for the gear, which is determined as one cycle for one rotationof the gear by such the magnetic sensor. Furthermore, a rotation angleof the rotation body is calculated, by a combination of each of therotation angle detection signals to be output from such the encoder andthe magnetic sensor individually.

[Patent Document 1] Japanese Patent Application Publication No.2001-505667

[Patent Document 2] Japanese Patent Application Publication No.2002-098522

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, there is a problem of low degree of freedom regarding designingaccording to the conventional rotation angle detection devices, becausethe phase difference between the detection signals is uniquelydetermined by such as a characteristic of the magnet to be provided ineach of the secondary rotation bodies, a gear ratio, or the like, thatare used for calculating the rotation angle of the rotation body.Moreover, there is a problem of becoming larger in size regarding adevice according to the conventional rotation angle detection devices,because it becomes required to design larger for a diameter of a gear ina case of widening a range of a detection angle for a rotation angle ofa detectable rotation body.

The present invention is presented with having regard to the abovementioned conventional problems, and an object is to provide a rotationangle detector to be able to realize a wide range of a detection angletherefor, with a high degree of freedom for designing thereof, withoutenlarging a device in size therefor.

Means for Solving the Problem

For solving the above mentioned subjects and achieving the object, arotation angle detector according to the present invention ischaracterized in that the rotation angle detector is for detecting arotation angle of a detectable rotation body, comprising: a primaryrotation body to be attached to the detectable rotation body and torotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa signal to be varied periodically as corresponding to a rotation of theprimary rotation body; a secondary rotation detection mechanism tooutput a signal to be varied periodically as corresponding to a rotationof the secondary rotation body; a signal processing unit to calculatethe rotation angles of the primary rotation body and the secondaryrotation body using the signals that the primary rotation detectionmechanism and the secondary rotation detection mechanism output; and anoperation processing unit to calculate the rotation angle of thedetectable rotation body, based on the calculated rotation angle of theprimary rotation body or of the secondary rotation body, and on arelative rotation angle between the primary rotation body and thesecondary rotation body, wherein at least any one of the followingsignals (A) to (D) is designed to have a cycle as different from onecycle for one rotation of the primary rotation body or of the secondaryrotation body;

(A) an output signal of the primary rotation detection mechanism;

(B) an output signal of the secondary rotation detection mechanism;

(C) an input signal from the primary rotation detection mechanism to beprocessed at the signal processing unit; and

(D) an input signal from the secondary rotation detection mechanism tobe processed at the signal processing unit.

Moreover, a rotation angle detector according to the present inventionis characterized in that the rotation angle detector is for detecting arotation angle of a detectable rotation body, comprising: a primaryrotation body to be attached to the detectable rotation body and torotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa signal to be varied periodically as corresponding to a rotation of theprimary rotation body; a secondary rotation detection mechanism tooutput a signal to be varied periodically as corresponding to a rotationof the secondary rotation body; a signal processing unit to convert acycle of the signals that the primary rotation detection mechanism andthe secondary rotation detection mechanism output, and to calculate therotation angles of the primary rotation body and the secondary rotationbody regarding the converted cycle by using the signals; and anoperation processing unit to calculate the rotation angle of thedetectable rotation body, based on the calculated rotation angle of theprimary rotation body or of the secondary rotation body, on a relativerotation angle between the primary rotation body and the secondaryrotation body, and on the converted cycle.

Further, a rotation angle detector according to the present invention ischaracterized in that the rotation angle detector is for detecting arotation angle of a detectable rotation body, comprising: a primaryrotation body to be attached to the detectable rotation body and torotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa continuous signal to be varied periodically as corresponding to arotation of the primary rotation body; a secondary rotation detectionmechanism to output a continuous signal to be varied periodically ascorresponding to a rotation of the secondary rotation body; a signalprocessing unit to calculate the rotation angles of the primary rotationbody and the secondary rotation body using the signals that the primaryrotation detection mechanism and the secondary rotation detectionmechanism output; and an operation processing unit to calculate therotation angle of the detectable rotation body, based on the calculatedrotation angle of the primary rotation body or of the secondary rotationbody, on a relative rotation angle between the primary rotation body andthe secondary rotation body, and on cycles of the signals that theprimary rotation detection mechanism and the secondary rotationdetection mechanism output.

Still further, a rotation angle detector according to the presentinvention is characterized in that the converted cycle regarding theabove described invention is determined as a cycle to be a desirablevalue for an allowable error of the rotation angle for each of theprimary rotation body or of the secondary rotation body, and for a rangeof a detection angle for the rotation angle of the detectable rotationbody.

Still further, a rotation angle detector according to the presentinvention is characterized in that the operation processing unitregarding the above described invention calculates a rotation angle Φ ofthe detectable rotation body using the following equations (1) to (4),with assuming the calculated rotation angle of the primary rotation bodyas θ1, an angle as θ2 of which the calculated rotation angle of thesecondary rotation body is multiplied by the predetermined rotationratio, the converted cycle of the signal of the primary rotationdetection mechanism as T1, a cycle as T2 (T1≠T2) of which the convertedcycle of the signal of the secondary rotation detection mechanism ismultiplied by the predetermined rotation ratio, an absolute value|T1−T2| as d for a difference between the cycle T1 and the T2;

in a case where T1<T2, and θ2≦θ1:Φ=θ1+T1(θ1−θ2)/d  (1);

in a case where T1<T2, and θ2>θ1:Φ=θ1+T1(θ1−θ2)/d+T1 T2/d  (2);

in a case where T1>T2, and θ1≦θ2:Φ=θ1+T1(θ2−θ1)/d  (3); and

in a case where T1>T2, and θ1>θ2:Φ=θ1+T1(θ2−θ1)/d+T1 T2/d  (4).

Still further, a rotation angle detector according to the presentinvention is characterized in that the rotation angle detector is fordetecting a rotation angle of a detectable rotation body, comprising: aprimary rotation body to be attached to the detectable rotation body andto rotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa continuous signal to be varied periodically as corresponding to arotation of the primary rotation body, with a periodicity of n as aninteger of not less than two for one rotation of the primary rotationbody; a secondary rotation detection mechanism to output a continuoussignal to be varied periodically as corresponding to a rotation of thesecondary rotation body, with a periodicity of m as an integer of lessthan n but not less than one for one rotation of the secondary rotationbody; a signal processing unit to calculate the rotation angles of theprimary rotation body and the secondary rotation body using the signalsthat the primary rotation detection mechanism and the secondary rotationdetection mechanism output; and an operation processing unit tocalculate the rotation angle of the detectable rotation body, based onthe calculated rotation angle of the primary rotation body or of thesecondary rotation body, on a relative rotation angle between theprimary rotation body and the secondary rotation body, and on cycles ofthe signals that the primary rotation detection mechanism and thesecondary rotation detection mechanism output.

Still further, a rotation angle detector according to the presentinvention is characterized in that the m regarding the above describedinvention is one.

Still further, a rotation angle detector according to the presentinvention is characterized in that the primary rotation detectionmechanism or the secondary rotation detection mechanism regarding theabove described invention comprises: a magnet to be attached to theprimary rotation body or to the secondary rotation body for generating amagnetic field of which intensity is varied continuously andperiodically in a rotation direction thereof; and two of magneticdetection elements to be arranged for having a predetermined anglearound a center of rotation for the primary rotation body or for thesecondary rotation body in a vicinity of the magnet.

Still further, a rotation angle detector according to the presentinvention is characterized in that the magnetic detection elementregarding the above described invention is a Hall element.

Furthermore, a rotation angle detector according to the presentinvention is characterized in that the magnetic detection elementregarding the above described invention is a magnetoresistive element.

EFFECT OF THE INVENTION

According to the present invention, it becomes able to obtain anadvantage that it becomes able to realize a rotation angle detector tobe able to realize a wide range of a detection angle therefor, with ahigh degree of freedom for designing thereof, without enlarging a devicein size therefor.

FIG. 1 is a cross sectional schematic diagram showing exemplary arotation angle detector according to the first embodiment regarding thepresent invention.

FIG. 2 is a block diagram showing a configuration of a primary rotationdetection mechanism, a secondary rotation detection mechanism, a signalprocessing unit and an operation processing unit as shown in FIG. 1.

FIG. 3 is a graph explaining a method for calculating a rotation angleof a primary gear regarding a rotation angle detector according to thefirst embodiment.

FIG. 4 is a graph explaining a method for calculating a rotation angleof a secondary gear regarding a rotation angle detector according to thefirst embodiment.

FIG. 5 is a graph explaining relations among angles θ1 and θ2, cycles T1and T2, a difference of cycles d, and a rotation angle Φ in a case whereθ2≦θ1 according to the first embodiment.

FIG. 6 is a drawing showing a cycle T2, a gear ratio and an allowableerror in a case where a cycle T1 is varied in a variety thereofregarding a range of a detection angle R as 1800 degrees according tothe first embodiment.

FIG. 7 is a flow diagram showing one example of a process flow for arotation angle Φ of a steering shaft X to be calculated according to thefirst embodiment.

FIG. 8 is a cross sectional schematic diagram showing exemplary arotation angle detector according to the second embodiment regarding thepresent invention.

FIG. 9 is a block diagram showing a configuration of a primary rotationdetection mechanism, a secondary rotation detection mechanism, a signalprocessing unit and an operation processing unit as shown in FIG. 8.

FIG. 10 is a graph explaining a method for calculating a rotation angleof a primary gear regarding a rotation angle detector according to thesecond embodiment.

FIG. 11 is a graph explaining a method for calculating a rotation angleof a secondary gear regarding a rotation angle detector according to thesecond embodiment.

FIG. 12 is a graph explaining relations among angles θ1 and θ2, cyclesT1 and T2, a difference of cycles d, and a rotation angle Φ in a casewhere θ2≦θ1 according to the second embodiment.

DESCRIPTION OF THE REFERENCE SYMBOLS

-   -   1, 101 ROTATION ANGLE DETECTOR    -   2, 102 PRIMARY GEAR    -   3, 103 SECONDARY GEAR    -   4, 104 PRIMARY ROTATION DETECTION MECHANISM    -   4 a, 104 a RING SHAPED MAGNET    -   4 b, 4 c, 104 b, 104 c HALL ELEMENT    -   5, 7, 105, 107 SIGNAL PROCESSING UNIT    -   6, 106 SECONDARY ROTATION DETECTION MECHANISM    -   6 a, 106 a DISK SHAPED MAGNET    -   6 b, 6 c, 106 b, 106 c HALL ELEMENT    -   8, 108 OPERATION PROCESSING UNIT    -   9, 109 HOUSING    -   A1 to A6, A101 to A106 AMPLIFIER    -   L1 to L12, L101 to L112 CURVED LINE    -   X STEERING SHAFT

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment regarding a rotation angle detector according to thepresent invention will be described in detail below, with reference tothe drawings. Here, according to the present embodiment, the presentinvention is not limited thereto.

The embodiment according to the present invention to be embodied asbelow is a rotation angle detector for detecting a rotation angle of adetectable rotation body which is characterized in that comprises: aprimary rotation body to be attached to the detectable rotation body andto rotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa signal to be varied periodically as corresponding to a rotation of theprimary rotation body; a secondary rotation detection mechanism tooutput a signal to be varied periodically as corresponding to a rotationof the secondary rotation body; a signal processing unit to calculatethe rotation angles of the primary rotation body and the secondaryrotation body using the signals that the primary rotation detectionmechanism and the secondary rotation detection mechanism output; and anoperation processing unit to calculate the rotation angle of thedetectable rotation body, based on the calculated rotation angle of theprimary rotation body or of the secondary rotation body, and on arelative rotation angle between the primary rotation body and thesecondary rotation body, wherein at least any one of the followingsignals (A) to (D) is designed to have a cycle as different from onecycle for one rotation of the primary rotation body or of the secondaryrotation body;

(A) an output signal of the primary rotation detection mechanism;

(B) an output signal of the secondary rotation detection mechanism;

(C) an input signal from the primary rotation detection mechanism to beprocessed at the signal processing unit; and

(D) an input signal from the secondary rotation detection mechanism tobe processed at the signal processing unit.

The First Embodiment

FIG. 1 is a cross sectional schematic diagram showing exemplary arotation angle detector according to the first embodiment regarding thepresent invention. Such the rotation angle detector according to thefirst embodiment is for detecting a rotation angle of a steering shaftin an automobile as a detectable rotation body.

Here, the rotation angle detector according to the first embodiment isone example that:

(C) an input signal from the primary rotation detection mechanism to beprocessed at the signal processing unit; and

(D) an input signal from the secondary rotation detection mechanism tobe processed at the signal processing unit are designed to have a cycleas different from one cycle for one rotation of the primary rotationbody or of the secondary rotation body, among the above mentionedsignals of (A) to (D).

As shown in FIG. 1, a rotation angle detector 1 comprises: a primarygear 2 of ring shape as a primary rotation body that a steering shaft Xas extended in a vertical direction to the page is attached and fixed byengaging in a hole at a central part thereof and rotates as integralwith the steering shaft X; a secondary gear 3 as a secondary rotationbody to mesh with the primary gear 2 and to rotate as a predeterminedrotation ratio for the primary gear 2; a primary rotation detectionmechanism 4 to output a signal to be varied periodically ascorresponding to a rotation of the primary gear 2; a signal processingunit 5 to convert a cycle of the signal that the primary rotationdetection mechanism 4 outputs and to calculate a rotation angle of theprimary gear 2 using such the signal; a secondary rotation detectionmechanism 6 to output a signal to be varied periodically ascorresponding to a rotation of the secondary gear 3; a signal processingunit 7 to convert a cycle of the signal that the secondary rotationdetection mechanism 6 outputs and to calculate a rotation angle of thesecondary gear 3 using such the signal; and an operation processing unit8 to calculate a rotation angle of the steering shaft X, based on thecalculated rotation angles of the primary gear 2 and the secondary gear3 that the signal processing units 5 and 7 calculate respectively, on arelative rotation angle between the primary gear 2 and the secondarygear 3, and on a converted cycle thereof. Here, a gear ratio between theprimary gear 2 and the secondary gear 3, that is to say, the rotationratio is 5/9. Moreover, a symbol 9 designates a housing of the rotationangle detector 1.

Further, the primary rotation detection mechanism 4 comprises: a magnet4 a of ring shape to be attached at the primary gear 2; and Hallelements 4 b and 4 c to be arranged at a position with a distance of 0.5mm for each thereof from a surface of the ring shaped magnet 4 a forhaving an angle of 90 degrees therebetween around a rotation center ofthe primary gear 2. As similar thereto, the secondary rotation detectionmechanism 6 comprises: a magnet 6 a of disk shape to be attached at thesecondary gear 3; and Hall elements 6 b and 6 c to be arranged at aposition with a distance of 0.5 mm for each thereof from a surface ofthe disk shaped magnet 6 a for having an angle of 90 degreestherebetween around a rotation center of the secondary gear 3. Stillfurther, the Hall elements 4 b, 4 c, 6 b and 6 c are fixed to therotation angle detector 1.

Still further, the ring shaped magnet 4 a is a dipoles magnet that apart of a south pole thereof and a part of a north pole thereof arealternately arranged for one part by one part, and is magnetized forgenerating a magnetic field that an intensity thereof is variedcontinuously and periodically as a sine wave shape in a rotationdirection of the primary gear 2. Still further, the Hall elements 4 band 4 c detect the magnetic field that the intensity thereof is variedcorresponding to the rotation of the primary gear 2, and thenindividually outputs a voltage signal corresponding to the intensity ofthe magnetic field. Still further, a cycle for a variation regarding theintensity of the magnetic field, that is to say, the cycle of thevoltage signal that the Hall elements 4 b and 4 c individually outputs,is 360 degrees. As similar thereto, the disk shaped magnet 6 a is adipoles magnet that a part of a south pole thereof and a part of a northpole thereof are alternately arranged for one part by one part, and ismagnetized for generating a magnetic field that an intensity thereof isvaried continuously and periodically as a sine wave shape in a rotationdirection of the secondary gear 3. Furthermore, the Hall elements 6 band 6 c detect the magnetic field that the intensity thereof is variedcorresponding to the rotation of the secondary gear 3, and thenindividually outputs a voltage signal corresponding to the intensity ofthe magnetic field of which cycle is 360 degrees respectively.

FIG. 2 is a block diagram showing a configuration of the primaryrotation detection mechanism 4, the secondary rotation detectionmechanism 6, the signal processing unit 5 and 7, and the operationprocessing unit 8, as shown in FIG. 1. Moreover, regarding the Hallelements 4 b and 4 c, a voltage is applied thereto which is amplified byusing an amplifier A1, that detect the magnetic field of the intensitycorresponding to the rotation of the primary gear 2, and then output thevoltage signals individually having a value of a voltage correspondingto the intensity of the magnetic field to be detected. Further,amplifiers A2 and A3 amplify the voltage signals that the Hall elements4 b and 4 c output, and then output S1 and S2 as values of the voltageto the signal processing unit 5 which comprises a microcontroller.Furthermore, the signal processing unit 5 obtains the voltage signal,performs an A/D conversion therefor, converts the cycle of the voltagesignal, calculates θ1 as the rotation angle of the primary gear 2 for acycle after the conversion, with using the values of voltage S1 and S2,and then outputs it to the operation processing unit 8 which comprises amicrocontroller.

As similar thereto, the Hall elements 6 b and 6 c to be applied avoltage, which is amplified by using an amplifier A4, output voltagesignals individually having a value of voltage corresponding to anintensity of the magnetic field to be detected thereby. Moreover, theamplifiers A5 and A6 amplify the voltage signals that the Hall elements6 b and 6 c output, and then output S3 and S4 as values of the voltageto the signal processing unit 7 which comprises a microcontroller.Further, the signal processing unit 7 obtains the voltage signal,performs an A/D conversion therefor, converts the cycle of the voltagesignal, calculates a rotation angle of the secondary gear 3 for a cycleafter the conversion using the values of voltage S3 and S4, calculatesθ2 as an angle that such the rotation angle is multiplied by therotation ratio of 5/9, and then outputs it to the operation processingunit 8. Furthermore, the operation processing unit 8 calculates arotation angle Φ of the steering shaft X with using the θ1 and the θ2.

Next, a method for detecting a rotation angle of the steering shaft X byusing the rotation angle detector 1 will be described in detail below,with reference to FIGS. 3 to 5. First, a method for calculating arotation angle of the primary gear 2 will be described in detail below,with reference to FIG. 3. Here, the S1 and the S2 as the values ofvoltage for the voltage signals to be input into the signal processingunit 5 correspond to each one point on sine curved lines L1 and L2respectively, that have cycles of 360 degrees as shown in such as agraph at an upper stage in FIG. 3 respectively. Here, regarding such thegraph, a horizontal axis therein indicates a rotation angle of theprimary gear 2 based on an arbitral position therefor, and a verticalaxis therein indicates a voltage of the voltage signal. Moreover, theHall element 4 b and 4 c are arranged to have the angle of 90 degreestherebetween around the rotation center of the primary gear 2, and thena phase difference of the sine curved lines L1 and the L2 becomes to be90 degrees.

Next, the signal processing unit 5 normalizes the values of voltage S1and the S2 by using the following equations (5) and (6). Here, values tobe normalized are assumed as M1 and M2; andM1=(S1−S1avg)/S1p  (5),M2=(S2−S2avg)/S2p  (6).

Here, the S1 avg and the S2 avg are average values of the maximum valueand the minimum value regarding one cycle of the voltage signalrespectively, and the S1 p and the S2 p are differences between themaximum value and the minimum value regarding the one cycle of thevoltage signal respectively. Moreover, regarding the S1 avg, the S2 avg,the S1 p and the S2 p, data of the voltage signals are obtained byrotating the primary gear 2 as one rotation at a time of assembling andadjusting the rotation angle detector 1, each of such the values areevaluated using such the data, and then those are memorized in thesignal processing unit 5. Further, the normalized values M1 and the M2to be evaluated in the above mentioned way individually correspond toeach one point on the sine curved lines L3 and the L4 having the cyclesof 360 degrees respectively, as shown in a graph at a middle stage inFIG. 3. Here, regarding such the graph, a horizontal axis thereinindicates a rotation angle of the primary gear 2 based on an arbitralposition therefor, and a vertical axis therein indicates a normalizedvalue.

Next, the signal processing unit 5 converts the cycle of the voltagesignal from 360 degrees to 180 degrees. As assuming a converted cycle tobe T1, T1=180 degrees. And then the signal processing unit 5 calculatesa θ1 as the rotation angle of the primary gear 2 at such the convertedcycle T1 by using the normalized values M1 and the M2. Here, it is ableto calculate the θ1 as below for example.

First, the θ is calculated by using equation (7).θ=Arctan(M1/M2)+α  (7).

Here, α=90 degrees in a case where M2>0, α=270 degrees in a case whereM2<0, meanwhile, θ=180 degrees in a case where M2=0 and M1>0, and θ=0degree in a case where M2=0 and M1<0.

And then it is assumed that θ1=θ if the θ is not larger than 180degrees, meanwhile, θ1=θ−180 if the θ is larger than 180 degrees.Moreover, it converts the cycle of 360 degrees to be the cycle of 180degrees as a half thereof.

According to the above mentioned method, the calculated angle θ1corresponds to the one point on a curved line of sawtooth shape L5having a cycle of 180 degrees as shown in a graph at a lower stage inFIG. 3. Here, regarding such the graph, a horizontal axis thereinindicates a rotation angle of the primary gear 2 based on an arbitralposition therefor, and a vertical axis therein indicates a calculatedrotation angle of the primary gear 2.

Next, a method for calculating a rotation angle of the secondary gear 3will be described in detail below, however, such the method is almostsimilar to the method for calculating the rotation angle of the primarygear 2. The S3 and the S4 as the values of voltage for the voltagesignals to be input into the signal processing unit 7 individuallycorrespond to each one point on sine curved lines L6 and L7respectively, that have cycles of 360 degrees as shown in such as agraph at an upper stage in FIG. 4 respectively. Here, regarding such thegraph, a horizontal axis therein indicates a rotation angle of thesecondary gear 3 based on an arbitral position therefor, and a verticalaxis therein indicates a voltage of the voltage signal. Moreover, aphase difference of the sine curved lines L6 and the L7 is 90 degrees.

Next, the signal processing unit 7 normalizes the voltage signals S3 andthe S4 to be as M3 and M4 respectively, by using the following equations(8) and (9).M3=(S3−S3avg)/S3p  (8),M4=(S4−S4avg)/S4p  (9).

Here, the S3 avg and the S4 avg are average values of the maximum valueand the minimum value for the voltage signal respectively, and the S3 pand the S4 p are differences between the maximum value and the minimumvalue for the voltage signal respectively. Moreover, data of the voltagesignals are obtained by rotating the secondary gear 3 as one rotation ata time of assembling and adjusting the rotation angle detector 1, eachof such the values are evaluated using such the data, and then those arememorized in the signal processing unit 7. Further, the normalizedvalues M3 and the M4 individually correspond to each one point on thesine curved lines L8 and the L9 having the cycles of 360 degreesrespectively, as shown in a graph at a middle stage in FIG. 4. Here,regarding such the graph, a horizontal axis therein indicates a rotationangle of the secondary gear 3 based on an arbitral position therefor,and a vertical axis therein indicates a normalized value.

Next, the signal processing unit 7 converts the cycle of the voltagesignal from 360 degrees to 360 degrees, and then multiplies the gearratio of 5/9. That is to say, as assuming a cycle to be as T2, that theconverted cycle is multiplied by the gear ratio, T2=360 5/9=200 degrees.Thus, according to the present invention, a conversion of a cycle of asignal includes a case of converting a cycle thereof to be as similar tothe cycle of itself.

Moreover, the signal processing unit 7 calculates a rotation angle ofthe secondary gear 3 at the cycle T2 by using the normalized values M3and the M4, and then calculates a θ2 as an angle that the rotation angleis multiplied by the gear ratio. Here, it is able to calculate the θ2 asbelow for example.

First, the θ is calculated by using an equation (10).θ=Arctan(M3/M4)+α  (10).

Here, α=90 degrees in a case where M4>0, α=270 degrees in a case whereM4<0, meanwhile, θ=180 degrees in a case where M4=0 and M3>0, and θ=0degree in a case where M4=0 and M3<0.

And then it calculates the θ2 using the θ to be multiplied by the gearratio of 5/9.

According to the above mentioned method, the calculated angle θ2corresponds to the one point on a curved line of sawtooth shape L10having a cycle of 200 degrees as shown in a graph at a lower stage inFIG. 4. Here, regarding such the graph, a horizontal axis thereinindicates a rotation angle of the secondary gear 3 based on an arbitralposition therefor, and a vertical axis therein indicates an angle thatthe calculated rotation angle of the secondary gear 3 is multiplied bythe gear ratio.

Next, the signal processing units 5 and 7 individually outputs theangles θ1 and the θ2 to the operation processing unit 8 respectively,which is evaluated as mentioned above. Here, according to the rotationangle detector 1 regarding the first embodiment, as T1=180 degrees andT2=200 degrees as mentioned above, the operation processing unit 8calculates Φ as the rotation angle of the steering shaft X, withassuming an absolute value as d=|T1−T2| for a difference of the cyclesbetween the cycle T1 and the T2, and by using the equations (1) and (2).

In a case where θ2≦θ1:Φ=θ1+T1(θ1−θ2)/d  (1),

In a case where θ2>θ1:Φ=θ1+T1(θ1−θ2)/d+T1 T2/d  (2).

Next, in the case where θ2≦θ1, relations among the angles θ1 and the θ2,the cycles T1 and the T2, the difference of the cycles d, and therotation angle Φ will be described in detail below, with reference toFIG. 5. Here, a horizontal axis in FIG. 5 indicates a range of adetection angle R=T1 T2/|T1−T2|=1800 degrees regarding the rotationangle of the steering shaft X. Moreover, a curved line L11 of sawtoothshape is the curved line L5 of sawtooth shape in FIG. 3 to be arrangedas ten cycles within the range of the detection angle R, wherein avertical axis therein indicates a ratio for the one cycle thereof, andthe ratio becomes to be 100% in a case where the angle is 180 degrees.While, a curved line L12 of sawtooth shape is the curved line L10 ofsawtooth shape in FIG. 4 to be arranged as nine cycles within the rangeof the detection angle R, wherein a vertical axis therein indicates aratio for the one cycle thereof, and the ratio is designed to be 100% ina case where the angle is 200 degrees. Further, regarding the rotationangle Φ, it is designed for a position thereof to be zero degree where aphase of the curved line L11 of sawtooth shape and of the L12 correspondto each other. In such a case, even at a position where Φ is 1800degrees, the phase of the curved line L11 of sawtooth shape and of theL12 correspond to each other.

Here for example, the angle θ1 and the θ2 are assumed to be calculatedindividually regarding the primary gear 2 and the secondary gear 3 asshown in FIG. 5. While, the rotation angle Φ is assumed to be calculatedby using the equation (1). In such a case, (θ1−θ2) as a relativerotation angle between the primary gear 2 and the secondary gear 3 meansa shift of the phases between the curved line L11 of sawtooth shape andthe L12. Moreover, because the curved line L11 of sawtooth shape and theL12 have the phases with the shift as the difference of the cycles d forevery rotation of the one cycle of the primary gear 2, (θ1−θ2)/d has avalue of integer, that is an equation meaning whether the rotation angleΦ includes rotations for how many times of cycles for the primary gear.More specifically, because the cycle T1 and the T2 regarding the primarygear 2 and the secondary gear 3 are 180 degrees and 200 degreesrespectively, the d becomes equal to 20 degrees. That is to say, in acase where the primary gear 2 rotates as one cycle, the phase becomes tobe shifted as 20 degrees for between the phase of the curved line L11 ofsawtooth shape and of the L12. According to FIG. 5, because the rotationangle Φ is the value that the primary gear further rotates as the angleof θ1 from a state that rotates as three cycles, (θ1−θ2)/d=3. Thus, theangles θ1 and the θ2, the cycles T1 and the T2, the difference of thecycles d, and the rotation angle Φ have the above mentioned relations,and then it becomes able to calculate the rotation angle Φ by using theequation (1).

On the contrary, in the case where θ2>θ1, the rotation angle Φ meanswhether including rotations for how many times of cycles for the primarygear, and then an equation becomes to be as [T2−(θ2−θ1)/d] which has avalue of integer. And then it becomes able to calculate the rotationangle Φ by using the equation (2).

Moreover, because the equation (1) and the following equation (1a), theequation (2) and the following equation (2a) are equivalent equationstherebetween respectively, it may be able to calculate the rotationangle Φ by using the equation (1a) in place of the equation (1), or itmay be able to calculate the rotation angle Φ by using the equation (2a)in place of the equation (2) as well.Φ=θ2+T2(θ1−θ2)/d  (1a),Φ=θ2+T2(θ1−θ2)/d+T1 T2/d  (2a).

As described above, the range of the detection angle R is expressed asR=T1 T2/|T1−T2|. That is to say, the detection angle R is the leastcommon denominator of the cycle T1 and the T2. And then it is requiredfor the cycle T1 and the T2 to be determined as a desirable range of thedetection angle R. Moreover, the difference of the cycles d is used fordetermining whether the rotation angle Φ includes rotations for how manycycles of the primary gear. And then an error to be allowed fordetecting the angles θ1 and the θ2 is expressed by the difference of thecycles d. Further, such the allowable error is set to be a desirablevalue with corresponding to such as an assembly tolerance of a rotationangle detecting device, a temperature characteristic thereof, or thelike. Therefore, it is required for the cycle T1 and the T2 to bedetermined as the desirable allowable error, that is to say, thedifference of the cycles d.

However, according to the rotation angle detector 1 regarding thepresent invention, it becomes able to obtain the desirable cycle T1 andthe T2 by converting the cycle of the voltage signal at the time of thesignal processing therefor. Therefore, it becomes able to determine thecycle T1 and the T2 for the difference of the cycles d and for the rangeof the detection angle R to be the desirable values respectively. As aresult, the range of the detection angle R and the difference of thecycles d become not to be fixed uniquely by such as the signal that theprimary rotation detection mechanism 4 and the secondary rotationdetection mechanism 6, the gear ratio, or the like, but it becomes ableto set those in a high degree of freedom respectively.

As described above, the rotation angle detector 1 according to the firstembodiment converts the cycle of the individual signals that the primaryrotation detection mechanism 4 and the secondary rotation detectionmechanism 6 output respectively, calculates the individual rotationangles of the primary gear 2 and the secondary gear 3 regarding thecycle to be converted by using such the signal, and then calculates therotation angle of the steering shaft X, based on the calculated rotationangle, on the relative rotation angle between the primary gear 2 and thesecondary gear 3, and on the cycle of the signal to be converted. As aresult, it becomes able to design in a high degree of freedomrespectively, regarding such as the primary rotation detectionmechanism, the secondary rotation detection mechanism, the gear ratiobetween the primary gear and the secondary gear, or the like.

Moreover, because the rotation angle detector 1 uses the secondary gearas just one, the detection error of the rotation is not superimposed asan error for the rotation angle of the primary gear 2, which isgenerated between the secondary gear 3 and the primary gear 2 due to abacklash of the gears. And then it becomes able to detect the rotationangle of the steering shaft X as further accurately. Further, it becomesable to reduce the number of component parts comparing to that of theconventional rotation angle detecting device, and then it becomes to bethe rotation angle detector of further small sized, with a lighterweight and a lower manufacturing cost therefor. Still further, becausethe rotation angle detector 1 uses the Hall element as the magneticdetection element, it becomes possible therefor to be as a furthersmaller in size, with a lighter weight and a lower manufacturing costtherefor.

Still further, regarding the rotation angle detector 1, the primaryrotation detection mechanism and the secondary rotation detectionmechanism are designed to output a continuous analog signal to be variedperiodically corresponding to the rotation of the primary gear 2 or thesecondary gear 3. Thus, it becomes able to design it smaller in sizecomparing to the case of the encoder to output the digital signal asdisclosed in the patent document 2. Furthermore, it becomes able toperform the angle detection with a higher resolution comparing to thecase of using a discrete digital signal, because of using the continuousanalog signal in the case of performing the detection of the rotationangle of the primary gear 2 and the secondary gear 3.

Next, in a case where the range of the detection angle R is 1800 degreesaccording to the first embodiment, the T2, the gear ratio and theallowable error will be shown in FIG. 6, in a case of varying the T1 ina variety thereof. Here, the equations (1) and (2) are used in the caseof calculating the rotation angle Φ of the steering shaft X, becauseT1<T2 according to the first embodiment. However, in a case where T1>T2due to the conversion of the cycle for the voltage signal, the rotationangle is calculated by using the following equations (3) and (4).

In a case where θ1≦θ2:Φ=θ1+T1(θ2−θ1)/d  (3); andin a case where θ1>θ2:Φ=θ1+T1(θ2−θ1)/d+T1 T2/d  (4).

In FIG. 6, the number of items [1] to [6] correspond to a case where thecycle T1 is 360/n (n is any integer of one to six) respectively. Here,because R=T1 T2/|T1−T2|, there are existed two of the T2 to be as T1<T2or T1>T2 corresponding to each of the T1 for satisfying R=1800. And thenthe gear ratio k=m T2/360 and the allowable error become to bedetermined for each of the T2. Here, m is the value that 360 is dividedby the cycle of the signal of the secondary rotation detectionmechanism. And it is assumed that m=1 according to FIG. 6.

Regarding the gear ratio, it becomes able to design the secondary gearas smaller in a case where it is smaller, and then it is desirablethereby because it becomes able to realize a smaller in size and alighter weight regarding the device. While, in a case where theallowable error is larger, it is desirable because an allowable amountbecomes larger regarding the detection error of the angles θ1 and the θ2due to the assembly tolerance of the device or the temperaturecharacteristic thereof. As shown in FIG. 6, there is a trade offrelation between the gear ratio and the allowable error. However,according to the rotation angle detector 1 regarding the firstembodiment, it becomes able to design the optimum values for the gearratio and the allowable error respectively, by converting the cycle ofthe signals of the primary rotation detection mechanism and thesecondary rotation detection mechanism.

Here, according to the first embodiment, there is used the Hall elementas the magnetic detection element, however, it may be also available touse a magnetoresistive element depend on the usage of the rotation angledetector, that has a temperature dependency as lower and has a higherangle resolution.

Moreover, according to the first embodiment, regarding the output signalof the primary rotation detection mechanism 4 and the output signal ofthe secondary rotation detection mechanism 6, it is designed to have onecycle for the one rotation of the primary gear 2 and of the secondarygear 3 respectively. However, it may be also available to designtherefor to have a different cycle therefrom respectively.

Here, according to the first embodiment, one example of a process flowfor the rotation angle Φ of the steering shaft X to be calculated willbe shown in FIG. 7. And, an equation or the like as shown in the flowdiagram of FIG. 7 is the equation or the like as expressed in the firstembodiment as described above. Moreover, the process flow as shown inFIG. 7 will be described in detail below. First, the signal processingunit 5 obtains the values of the voltage S1 and the S2, and also thesignal processing unit 7 obtains the values of the voltage S3 and the S4(a step ST101). Next, the signal processing unit 5 performs an A/Dconversion for the values of the voltage S1 and the S2, and also thesignal processing unit 7 performs an A/D conversion for the values ofthe voltage S3 and the S4 (a step ST102). Next, the signal processingunit 5 calculates the normalized values M1 and the M2 (a step ST103),and then calculates the angle θ1 (a step ST104). Next, the signalprocessing unit 7 calculates the normalized values M3 and the M4 (a stepST105), and then calculates the angle θ2 (a step ST106). Next, theoperation processing unit 8 calculates the angle Φ (a step ST107), andthen outputs the angle Φ (a step ST108). Further, it repeats the stepST101 thorough the step ST108 thereafter. Here, it is needless to saythat the flow of the signal processing according to the first embodimentis not limited to such the process flow. Furthermore, for the secondembodiment as described below, a processing as almost similar to theflow diagram of FIG. 7 is performed.

The Second Embodiment

FIG. 8 is a cross sectional schematic diagram showing exemplary arotation angle detector according to the second embodiment regarding thepresent invention. Such the rotation angle detector according to thesecond embodiment is for detecting a rotation angle of a steering shaftin an automobile as a detectable rotation body, as similar to thataccording to the first embodiment.

Here, the rotation angle detector according to the second embodiment isone example, wherein at least either one of:

(A) an output signal of the primary rotation detection mechanism; or

(B) an output signal of the secondary rotation detection mechanism,among the above mentioned signals (A) to (D) is designed to be asdifferent from the one cycle for the one rotation of the primaryrotation body or of the secondary rotation body.

As shown in FIG. 8, a rotation angle detector 101 comprises: a primarygear 102 of ring shape as a primary rotation body that a steering shaftX as extended in a vertical direction to the page is attached and fixedby engaging in a hole at a central part thereof and rotates as integralwith the steering shaft X; a secondary gear 103 as a secondary rotationbody to mesh with the primary gear 102 and to rotate as a predeterminedrotation ratio for the primary gear 102; a primary rotation detectionmechanism 104 to output a continuous signal to be varied periodically ascorresponding to a rotation of the primary gear 102; a signal processingunit 105 to calculate a rotation angle of the primary gear 102 using thesignal that the primary rotation detection mechanism 104 outputs; asecondary rotation detection mechanism 106 to output a continuous signalto be varied periodically as corresponding to a rotation of thesecondary gear 103; a signal processing unit 107 to calculate a rotationangle of the secondary gear 103 using the signal that the secondaryrotation detection mechanism 106 outputs; and an operation processingunit 108 to calculate a rotation angle of the steering shaft X, based onthe calculated rotation angles of the primary gear 102 and the secondarygear 103 that the signal processing units 105 and 107 calculaterespectively, on a relative rotation angle between the primary gear 102and the secondary gear 103, and on the cycle of the signals that theprimary rotation detection mechanism 104 and the secondary rotationdetection mechanism 106 output respectively. Here, a gear ratio betweenthe primary gear 102 and the secondary gear 103, that is to say, therotation ratio is assumed to be as 5/9. Moreover, a symbol 109designates a housing of the rotation angle detector 101.

Further, the primary rotation detection mechanism 104 comprises: amagnet 104 a of ring shape to be attached at the primary gear 102; andHall elements 104 b and 104 c to be arranged at a position with adistance of 0.5 mm for each thereof from a surface of the ring shapedmagnet 104 a for having an angle of 45 degrees therebetween around arotation center of the primary gear 102. As similar thereto, thesecondary rotation detection mechanism 106 comprises: a magnet 106 a ofdisk shape to be attached at the secondary gear 103; and Hall elements106 b and 106 c to be arranged at a position with a distance of 0.5 mmfor each thereof from a surface of the disk shaped magnet 106 a forhaving an angle of 90 degrees therebetween around a rotation center ofthe secondary gear 103. Still further, the Hall elements 104 b, 104 c,106 b and 106 c are fixed to the rotation angle detector 101.

Still further, the ring shaped magnet 104 a is a quadrupoles magnet thata part of a south pole thereof and a part of a north pole thereof arealternately arranged for two parts by two parts, and is magnetized forgenerating a magnetic field that an intensity thereof is variedcontinuously and periodically as a sine wave shape in a rotationdirection of the primary gear 102, and that is designed to be generatedas two cycles for one rotation thereof. Still further, the Hall elements104 b and 104 c detect the magnetic field that the intensity thereof isvaried corresponding to the rotation of the primary gear 102, and thenindividually outputs a voltage signal corresponding to the intensity ofthe magnetic field with two cycles for one rotation thereof, that is tosay, with a periodicity as two. Still further, a cycle for a variationregarding the intensity of the magnetic field, that is to say, the cycleof the voltage signal that the Hall elements 104 b and 104 cindividually outputs, is 180 degrees as a value that 360 degrees isdivided by the periodicity of two. While, the disk shaped magnet 106 ais a dipoles magnet that a part of a south pole thereof and a part of anorth pole thereof are alternately arranged for one part by one part,and is magnetized for generating a magnetic field that an intensitythereof is varied continuously and periodically as a sine wave shape ina rotation direction of the secondary gear 103. Furthermore, the Hallelements 106 b and 106 c detect the magnetic field that the intensitythereof is varied corresponding to the rotation of the secondary gear103, and then individually outputs a voltage signal with a periodicityas one, with corresponding to the intensity of the magnetic fieldrespectively. That is to say, the individual cycles that the Hallelements 106 b and 106 c output is 360 degrees as a value that 360degrees is divided by the periodicity of one.

Therefore, as assuming the periodicity of the continuous signal to be n,that the primary rotation detection mechanism 104 of the rotation angledetector 101 outputs, and as assuming the periodicity of the continuoussignal to be m, that the secondary rotation detection mechanism 106outputs, n=2, m=1. As described later, the smaller an absolute value ofa difference between the cycle of the signal that the primary rotationdetection mechanism 104 outputs and a cycle to be obtained bymultiplying a gear ratio onto the cycle of the signal that the secondaryrotation detection mechanism 106 outputs, the larger a range of adetection angle becomes, which is for the rotation of the shaft X of therotation angle detector 101. Thus, the rotation angle detector 101becomes to have the range of the detection angle as further wider.

Next, such the rotation angle detector 101 will be further described indetail below. FIG. 9 is a block diagram showing a configuration of theprimary rotation detection mechanism 104, the secondary rotationdetection mechanism 106, the signal processing unit 105 and 107, and theoperation processing unit 108, as shown in FIG. 8. Moreover, regardingthe Hall elements 104 b and 104 c, a voltage is applied thereto which isamplified by using an amplifier A101, that detect the magnetic field ofthe intensity corresponding to the rotation of the primary gear 102, andthen output the voltage signals individually having a value of a voltagecorresponding to the intensity of the magnetic field to be detected.Further, amplifiers A102 and A103 amplify the voltage signals that theHall elements 104 b and 104 c output respectively, determined thereforto be S101 and S102 as values of the voltage respectively, and thenoutput to the signal processing unit 105 which comprises amicrocontroller. Furthermore, the signal processing unit 105 obtains thevoltage signal, performs an A/D conversion therefor, calculates a θ101as the rotation angle of the primary gear 102 with using the values ofvoltage S101 and S102, and then outputs it to the operation processingunit 108 which comprises a microcontroller.

As similar thereto, the Hall elements 106 b and 106 c to be applied avoltage, which is amplified by using an amplifier A104, output voltagesignals individually having a value of voltage corresponding to anintensity of the magnetic field to be detected thereby. Moreover, theamplifiers A105 and A106 amplify the voltage signals that the Hallelements 106 b and 106 c output respectively, determine those to be S103and S104 as values of the voltage respectively, and then output those tothe signal processing unit 107 which comprises a microcontroller.Further, the signal processing unit 107 obtains the voltage signal,performs an A/D conversion therefor, calculates a rotation angle of thesecondary gear 103 with using the values of voltage S103 and S104,calculates a θ102 as an angle that such the rotation angle is multipliedby the rotation ratio of 5/9, and then outputs it to the operationprocessing unit 108. Furthermore, the operation processing unit 108calculates a rotation angle Φ of the steering shaft X with using theθ101 and the θ102.

Next, a method for detecting a rotation angle of the steering shaft X byusing the rotation angle detector 101 will be described in detail below,with reference to FIGS. 10 to 12. First, a method for calculating arotation angle of the primary gear 102 will be described in detailbelow, with reference to FIG. 10. Here, the S101 and the S102 as thevalues of voltage for the voltage signals to be input into the signalprocessing unit 105 correspond to each one point on sine curved linesL101 and L102 respectively, that have cycles of 180 degrees as shown insuch as a graph at an upper stage in FIG. 10 respectively. Here,regarding such the graph, a horizontal axis therein indicates a rotationangle of the primary gear 102 based on an arbitral position therefor,and a vertical axis therein indicates a voltage of the voltage signal.Moreover, the Hall element 104 b and 104 c are arranged to have theangle of 45 degrees therebetween around the rotation center of theprimary gear 102, and then a phase difference of the sine curved linesL101 and the L102 becomes to be 45 degrees.

Next, the signal processing unit 105 normalizes the values of voltageS101 and the S102 by using the following equations (101) and (102).Here, values to be normalized are assumed as M101 and M102; andM1=(S101−S101avg)/S101p  (101),M2=(S102−S102avg)/S102p  (102).

Here, the S101 avg and the S102 avg are average values of the maximumvalue and the minimum value regarding one cycle of the voltage signalrespectively, and the S101 p and the S102 p are differences between themaximum value and the minimum value regarding the one cycle of thevoltage signal respectively. Moreover, regarding the S101 avg, the S102avg, the S101 p and the S102 p, data of the voltage signals are obtainedby rotating the primary gear 102 as one rotation at a time of assemblingand adjusting the rotation angle detector 101, each of such the valuesare evaluated using such the data, and then those are memorized in thesignal processing unit 105. Further, the normalized values M101 and theM102 to be evaluated in the above mentioned way individually correspondto each one point on the sine curved lines L103 and the L104 having thecycles of 180 degrees respectively, as shown in a graph at a middlestage in FIG. 10. Here, regarding such the graph, a horizontal axistherein indicates a rotation angle of the primary gear 102 based on anarbitral position therefor, and a vertical axis therein indicates anormalized value.

Next, the signal processing unit 105 calculates the θ101 as the rotationangle of the primary gear 102 by using the normalized values M101 andthe M102. Here, it is able to calculate the θ101 as below for example.

First, the θ101 is calculated by using an equation (103).θ101=0.5 Arctan(M101/M102)+α  (103).

Here, α=45 degrees in a case where M102>0, α=135 degrees in a case whereM102<0, meanwhile, θ101=90 degrees in a case where M102=0 and M101>0,and θ101=0 degree in a case where M102=0 and M101<0.

According to the above mentioned method, the calculated angle θ101corresponds to the one point on a curved line of sawtooth shape L105having a cycle of 180 degrees as shown in a graph at a lower stage inFIG. 10. Here, regarding such the graph, a horizontal axis thereinindicates a rotation angle of the primary gear 102 based on an arbitralposition therefor, and a vertical axis therein indicates a calculatedrotation angle of the primary gear 102.

Next, a method for calculating a rotation angle of the secondary gear103 will be described in detail below, however, such the method isalmost similar to the method for calculating the rotation angle of theprimary gear 102. The S103 and the S104 as the values of voltage for thevoltage signals to be input into the signal processing unit 107individually correspond to each one point on sine curved lines L106 andL107 respectively, that have cycles of 360 degrees as shown in such as agraph at an upper stage in FIG. 11 respectively. Here, regarding suchthe graph, a horizontal axis therein indicates a rotation angle of thesecondary gear 103 based on an arbitral position therefor, and avertical axis therein indicates a voltage of the voltage signal.Moreover, a phase difference between the sine curved lines L106 and theL107 is 90 degrees.

Next, the signal processing unit 107 normalizes the voltage signals S103and the S104 to be as M103 and M104 respectively, by using the followingequations (104) and (105).M103=(S103−S103avg)/S103p  (104),M104=(S104−S104avg)/S104p  (105).

Here, the S103 avg and the S104 avg are average values of the maximumvalue and the minimum value for the voltage signal respectively, and theS103 p and the S104 p are differences between the maximum value and theminimum value for the voltage signal respectively. Moreover, data of thevoltage signals are obtained by rotating the secondary gear 103 as onerotation at a time of assembling and adjusting the rotation angledetector 101, each of such the values are evaluated using such the data,and then those are memorized in the signal processing unit 107. Further,the normalized values M103 and the M104 individually correspond to eachone point on the sine curved lines L108 and the L109 having the cyclesof 360 degrees respectively, as shown in a graph at a middle stage inFIG. 11. Here, a horizontal axis therein indicates a rotation angle ofthe secondary gear 103 based on an arbitral position therefor, and avertical axis therein indicates a normalized value.

Next, the signal processing unit 107 calculates a rotation angle of thesecondary gear 103 by using the normalized values M103 and the M104, andthen calculates the θ102 as the angle that the rotation angle ismultiplied by the gear ratio. Here, it is able to calculate the θ102 asbelow for example.

First, the θ is calculated by using an equation (106).θ=Arctan(M103/M104)+α  (106).

Here, α=90 degrees in a case where M104>0, α=270 degrees in a case whereM104<0, meanwhile, θ=180 degrees in a case where M104=0 and M103>0, andθ=0 degree in a case where M104=0 and M103<0.

And then it calculates the θ102 using the θ to be multiplied by the gearratio of 5/9.

According to the above mentioned method, the calculated angle θ102corresponds to the one point on a curved line of sawtooth shape L110having a cycle of 200 degrees as shown in a graph at a lower stage inFIG. 11. Here, regarding such the graph, a horizontal axis thereinindicates a rotation angle of the secondary gear 103 based on anarbitral position therefor, and a vertical axis therein indicates anangle that the calculated rotation angle of the secondary gear 103 ismultiplied by the gear ratio.

Next, the signal processing units 105 and 107 individually outputs theangles θ101 and the θ102 to the operation processing unit 108respectively, which is evaluated as mentioned above. Here, according tothe rotation angle detector 101 regarding the second embodiment, as thecycle T101 is 180 degrees, of which the primary rotation detectionmechanism 104 outputs the signal, and the cycle T102 is 200 degrees,which is obtained by multiplying the gear ratio of 5/9 onto the cycle ofthe signal that the secondary rotation detection mechanism 106 outputs,as mentioned above. And then the operation processing unit 108calculates the Φ as the rotation angle of the steering shaft X, withassuming an absolute value as d=|T101−T102| for a difference of thecycles between the cycle T101 and the T102, and by using the followingequations (107) and (108).

In a case where θ102≦θ101:Φ=θ101+T101(θ101−θ102)/d  (107),

In a case where θ102>θ101:Φ=θ101+T101(θ101−θ102)/d+T101 T102/d  (108).

Next, in the case where θ102≦θ101, relations among the angles θ101 andthe θ102, the cycles T101 and the T102, the difference of the cycles d,and the rotation angle Φ will be described in detail below, withreference to FIG. 12. Here, a horizontal axis in FIG. 12 indicates arange of a detection angle R=T101 T102/|T101−T102|=1800 degreesregarding the rotation angle of the steering shaft X. Moreover, a curvedline L111 of sawtooth shape is the curved line L105 of sawtooth shape inFIG. 10 to be arranged as ten cycles within the range of the detectionangle R, wherein a vertical axis therein indicates a ratio for the onecycle thereof, and the ratio becomes to be 100% in a case where theangle is 180 degrees. While, a curved line L112 of sawtooth shape is thecurved line L110 of sawtooth shape in FIG. 11 to be arranged as ninecycles within the range of the detection angle R, wherein a verticalaxis therein indicates a ratio for the one cycle thereof, and the ratiois designed to be 100% in a case where the angle is 200 degrees.Further, regarding the rotation angle Φ, it is designed for a positionthereof to be zero degree where a phase of the curved line L111 ofsawtooth shape and of the L112 correspond to each other. In such a case,even at a position where the Φ is 1800 degrees, the phase of the curvedline L111 of sawtooth shape and of the L112 correspond to each other.

Here for example, the angle θ101 and the θ102 are assumed to becalculated individually regarding the primary gear 102 and the secondarygear 103 as shown in FIG. 12. While, the rotation angle Φ is assumed tobe calculated by using the equation (107). In such a case, (θ101−θ102)as a relative rotation angle between the primary gear 102 and thesecondary gear 103 means a shift of the phases between the curved lineL111 of sawtooth shape and the L112. Moreover, because the curved lineL111 of sawtooth shape and the L112 have the phases with the shift asthe difference of the cycles d for every rotation of the one cycle ofthe primary gear 102, (θ101−θ102)/d has a value of integer, that is anequation meaning whether the rotation angle Φ includes rotations for howmany times of cycles for the primary gear. More specifically, becausethe cycle T101 and the T102 regarding the primary gear 102 and thesecondary gear 103 are 180 degrees and 200 degrees respectively, the dbecomes equal to 20 degrees. That is to say, in a case where the primarygear 102 rotates as one cycle, the phase becomes to be shifted as 20degrees for between the phase of the curved line L111 of sawtooth shapeand of the L112. According to FIG. 12, because the rotation angle Φ isthe value that the primary gear further rotates as the angle of θ101from a state that rotates as three cycles, (θ101−θ102)/d=3. Thus, theangles θ101 and the θ102, the cycles T101 and the T102, the differenceof the cycles d, and the rotation angle Φ have the above mentionedrelations, and then it becomes able to calculate the rotation angle Φ byusing the equation (107). On the contrary, in the case where θ102>θ101,the rotation angle Φ means whether including rotations for how manytimes of cycles for the primary gear, and then an equation becomes to beas [T102−(θ102−θ101)]/d which has a value of integer. And then itbecomes able to calculate the rotation angle Φ by using the equation(108).

Thus, the range of the detection angle R is determined by R=T101T102/|T101−T102|, and the gear ratio k is determined by k=T102 m/360.Hence, the smaller and the smaller the |T101−T102| is, the larger the Rbecomes, and then the range of the detection becomes to be wider.Therefore, it is necessary to make a difference between the values ofthe T101 and the T102 to be smaller by bringing close to each other fordesigning the R to be larger. However, a gear ratio becomes to be largerin a case where the T101 is large, that is to say, the periodicity of nis one and the T101 is 360 degrees for example, or the m is large, andthen a gear cannot help but become to be larger in size. For example,according to the above mentioned conventional rotation angle detectingdevice, in the case where each of the periodicities of the primary gearand the secondary gear is one, that is to say, n=m=1, it is required fora gear ratio to be 5/4 or 5/6 in a case of setting a range of adetection angle R to be 1800 degrees, and then it becomes required for asize of the secondary gear 106 to be as approximately similar to that ofthe primary gear 102. While, the primary gear 102 is fixed to thesteering shaft X by engaging thereto, and then there is a limitationregarding designing the primary gear to be smaller in size. Hence, itcannot help but design the secondary gear to be larger for realizing theabove mentioned gear ratio, and then the device becomes to be larger insize thereby. However, according to the rotation angle detector 101, theperiodicity of n is determined as two for the continuous signal that theprimary rotation detection mechanism 104 outputs, and the periodicity ofm is determined as one for the continuous signal that the secondaryrotation detection mechanism 106 outputs. Thus, it becomes able to setthe secondary gear 103 in the range of detection as similar to eachother. While, it is desirable for the m to be one as possible, as itbecomes easier to design a configuration of the rotation detectionmechanisms.

As above described, according to the rotation angle detector 101regarding the second embodiment, it becomes able to realize the widerrange of the detection angle without designing the device to be largerin size. Moreover, according to the rotation angle detector 101, theprimary rotation detection mechanism 104 and the secondary rotationdetection mechanism 106 are designed to output individually thecontinuous analog signals which is varied periodically as correspondingto the rotation of the primary gear 102 or the secondary gear 103. Thus,it becomes able to design it to be smaller in size comparing to the caseof using the conventional encoder which outputs the digital signal,because it becomes unnecessary to use a rotor of disk shape that aplurality of slits are formed. Further, according to the secondembodiment, it becomes possible to perform an angle detection with ahigher resolution in a case where a periodicity is larger and a cyclethereof is shorter as possible regarding a voltage signal that a primaryrotation detection mechanism outputs. The reason is because that aresolution of an A/D conversion is fixed to be as ten bits in a fullscale for example in a case of inputting a voltage signal, whichcorresponds to an angle to be detected, into a microcontroller, and thena range of an angle becomes to be smaller, which is to be detected withusing ten bits as similar thereto in a case where the shorter the cycleof the voltage signal is. Still further, according to the rotation angledetector 101, it becomes possible to design a further smaller in sizethereof, a lighter weight thereof, and a lower manufacturing costtherefor, because the Hall element is used therefor as the magneticdetection element.

Still further, according to the second embodiment, because the equation(107) and the following equation (107a), the equation (108) and thefollowing equation (108a) are equivalent equations therebetweenrespectively, it may be able to calculate the rotation angle Φ by usingthe equation (107a) in place of the equation (107), or it may be able tocalculate the rotation angle Φ by using the equation (108a) in place ofthe equation (108) as well.Φ=θ102+T102(θ101−θ102)/d  (107a),Φ=θ102+T102(θ101−θ102)/d+T101 T102/d  (108a).

Still further, the equations (107) and (108) are used in the case ofcalculating the rotation angle Φ of the steering shaft X, becauseT101<T102 according to the second embodiment. However, in a case whereT101>T102, it is able to calculate a rotation angle by using thefollowing equations (109) and (110).

In a case where θ101<θ102:Φ=θ101+T101(θ102−θ101)/d  (109);and in a case where θ101>θ102:Φ=θ101+T101(θ102−θ101)/d+T101 T102/d  (110).

Still further, according to the above described embodiment, there isused the Hall element as the magnetic detection element, however, it maybe also available to use a magnetoresistive element depend on the usageof the rotation angle detector, that has a temperature dependency aslower and has a higher angle resolution.

Still further, as a modified example of the above described secondembodiment, as assuming that the range of the detection angle R is 1800degrees, that the periodicity of m is one, and that the periodicity of nis three, the T102 becomes to be 112.5 and a gear ratio becomes to be5/16, and then it becomes able to design a secondary gear to be furthersmaller in size. Still further, for the n to be determined as three, itmay be available to use a hexa-poles magnet as a magnet of ring shape tobe attached to a primary gear, that a part of a south pole thereof and apart of a north pole thereof are alternately arranged for three parts bythree parts, and is magnetized for generating a magnetic field that anintensity thereof is varied continuously and periodically as a sine waveshape in a rotation direction of the primary gear, and that is designedto be generated as three cycles for one rotation thereof. Here, the m isnot limited to one, and it is able to design it to have a value of notless than two but smaller than the n. However, it is desirable to designit as one for designing a secondary gear to be smaller in size. Stillfurther, it is able to set easily the values of the n and the m to bevalues as desirable respectively, by arranging properly a part of asouth pole of a magnet and a part of a north pole thereof to be attachedto a primary gear or a secondary gear.

Still further, each of the above described embodiments is the rotationangle detector for which the devices are used as the primary rotationdetection mechanism and as the secondary rotation detection mechanismthat individually outputs the continuous analog signal. However, it maybe also available to use a rotation angle detector for which a device isused as a primary rotation detection mechanism or as a secondaryrotation detection mechanism, such as an encoder or the like thatoutputs a digital signal, and then for performing a signal processingthe digital signal to be output therefrom. Furthermore, it is possibleto adopt an embodiment which is combined the first embodiment and thesecond embodiment as well.

INDUSTRIAL APPLICABILITY

It is able to use preferably the rotation angle detector according tothe present invention for a case of detecting a rotation angle of adetectable rotation body, such as a steering shaft of an automobile orthe like.

1. A rotation angle detector for detecting a rotation angle of adetectable rotation body, comprising: a primary rotation body to beattached to the detectable rotation body and to rotate as integral withthe detectable rotation body; a secondary rotation body to rotate as apredetermined rotation ratio for the primary rotation body; a primaryrotation detection mechanism to output a signal to be variedperiodically as corresponding to a rotation of the primary rotationbody; a secondary rotation detection mechanism to output a signal to bevaried periodically as corresponding to a rotation of the secondaryrotation body; a signal processing unit to calculate the rotation anglesof the primary rotation body and the secondary rotation body using thesignals that the primary rotation detection mechanism and the secondaryrotation detection mechanism output; and an operation processing unit tocalculate the rotation angle of the detectable rotation body, based onthe calculated rotation angle of the primary rotation body or of thesecondary rotation body, and on a relative rotation angle between theprimary rotation body and the secondary rotation body, wherein theoperation processing unit calculates a rotation angle φ of thedetectable rotation body using the following equations (1) to (4), withassuming the calculated rotation angle of the primary rotation body asθ1, an angle as θ2 of which the calculated rotation angle of thesecondary rotation body is multiplied by the predetermined rotationratio, the converted cycle of the first signal of the primary rotationdetection mechanism as T1, a cycle as T2 (T1≠T2) of which the convertedcycle of the second signal of the secondary rotation detection mechanismis multiplied by the predetermined rotation ratio, an absolute value|T1−T2| as d for a difference between the cycle T1 and the T2; in a casewhere T1<T2, and θ2≦θ1:Φ=θ1+T1(θ1−θ2)/d  (1); in a case where T1<T2, and θ2>θ1:Φ=θ1+T1(θ1−θ2)/d+T1T2/d  (2); in a case where T1>T2, and θ1≦θ2:Φ=θ1+T1(θ2−θ1)/d  (3); and in a case where T1>T2, and θ1>θ2:Φ=θ1+T1(θ2−θ1)/d+T1T2/d  (4).
 2. A rotation angle detector for detectinga rotation angle of a detectable rotation body, comprising: a primaryrotation body to be attached to the detectable rotation body and torotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa signal to be varied periodically as corresponding to a rotation of theprimary rotation body; a secondary rotation detection mechanism tooutput a signal to be varied periodically as corresponding to a rotationof the secondary rotation body; a signal processing unit to convert acycle of the signals that the primary rotation detection mechanism andthe secondary rotation detection mechanism output, and to calculate therotation angles of the primary rotation body and the secondary rotationbody regarding the converted cycle by using the signals; and anoperation processing unit to calculate the rotation angle of thedetectable rotation body, based on the calculated rotation angle of theprimary rotation body or of the secondary rotation body, on a relativerotation angle between the primary rotation body and the secondaryrotation body, and on the converted cycle, wherein the operationprocessing unit calculates a rotation angle Φ of the detectable rotationbody using the following equations (1) to (4), with assuming thecalculated rotation angle of the primary rotation body as θ1, an angleas θ2 of which the calculated rotation angle of the secondary rotationbody is multiplied by the predetermined rotation ratio, the convertedcycle of the signal of the primary rotation detection mechanism as T1, acycle as T2 (T1≠T2) of which the converted cycle of the signal of thesecondary rotation detection mechanism is multiplied by thepredetermined rotation ratio, an absolute value |T1−T2| as d for adifference between the cycle T1 and the T2; in a case where T1<T2, andθ2≦θ1:Φ=θ1+T1(θ1−θ2)/d  (1); in a case where T1<T2, and θ2>θ1:Φ=θ1+T1(θ1−θ2)/d+T1T2/d  (2); in a case where T1>T2, and θ1≦θ2:Φ=θ1+T1(θ2−θ1)/d  (3); and in a case where T1>T2, and θ1>θ2:Φ=θ1+T1(θ2−θ1)/d+T1T2/d  (4).
 3. The rotation angle detector accordingto claim 2, wherein the converted cycle is determined as a cycle to be adesirable value for an allowable error of the rotation angle for each ofthe primary rotation body or of the secondary rotation body, and for arange of a detection angle for the rotation angle of the detectablerotation body.
 4. A rotation angle detector for detecting a rotationangle of a detectable rotation body, comprising: a primary rotation bodyto be attached to the detectable rotation body and to rotate as integralwith the detectable rotation body; a secondary rotation body to rotateas a predetermined rotation ratio for the primary rotation body; aprimary rotation detection mechanism to output a continuous signal to bevaried periodically as corresponding to a rotation of the primaryrotation body; a secondary rotation detection mechanism to output acontinuous signal to be varied periodically as corresponding to arotation of the secondary rotation body; a signal processing unit tocalculate the rotation angles of the primary rotation body and thesecondary rotation body using the signals that the primary rotationdetection mechanism and the secondary rotation detection mechanismoutput; and an operation processing unit to calculate the rotation angleof the detectable rotation body, based on the calculated rotation angleof the primary rotation body or of the secondary rotation body, on arelative rotation angle between the primary rotation body and thesecondary rotation body, and on cycles of the signals that the primaryrotation detection mechanism and the secondary rotation detectionmechanism output, wherein the operation processing unit calculates arotation angle Φ of the detectable rotation body using the followingequations (1) to (4), with assuming the calculated rotation angle of theprimary rotation body as θ1, an angle as θ2 of which the calculatedrotation angle of the secondary rotation body is multiplied by thepredetermined rotation ratio, the converted cycle of the continuoussignal of the primary rotation detection mechanism as T1, a cycle as T2(T1≠T2) of which the converted cycle of the continuous signal of thesecondary rotation detection mechanism is multiplied by thepredetermined rotation ratio, an absolute value |T1−T2| as d for adifference between the cycle T1 and the T2; in a case where T1<T2, andθ2≦θ1:Φ=θ1+T1(θ1−θ2)/d  (1); in a case where T1<T2, and θ2>θ1:Φ=θ1+T1(θ1−θ2)/d+T1T2/d  (2); in a case where T1>T2, and θ1≦θ2:Φ=θ1+T1(θ2−θ1)/d  (3); and in a case where T1>T2, and θ1>θ2:Φ=θ1+T1(θ2−θ1)/d+T1T2/d  (4).
 5. A rotation angle detector for detectinga rotation angle of a detectable rotation body, comprising: a primaryrotation body to be attached to the detectable rotation body and torotate as integral with the detectable rotation body; a secondaryrotation body to rotate as a predetermined rotation ratio for theprimary rotation body; a primary rotation detection mechanism to outputa continuous signal to be varied periodically as corresponding to arotation of the primary rotation body, with a periodicity of n as aninteger of not less than two for one rotation of the primary rotationbody; a secondary rotation detection mechanism to output a continuoussignal to be varied periodically as corresponding to a rotation of thesecondary rotation body, with a periodicity of m as an integer of lessthan n but not less than one for one rotation of the secondary rotationbody; a signal processing unit to calculate the rotation angles of theprimary rotation body and the secondary rotation body using the signalsthat the primary rotation detection mechanism and the secondary rotationdetection mechanism output; and an operation processing unit tocalculate the rotation angle of the detectable rotation body, based onthe calculated rotation angle of the primary rotation body or of thesecondary rotation body, on a relative rotation angle between theprimary rotation body and the secondary rotation body, and on cycles ofthe signals that the primary rotation detection mechanism and thesecondary rotation detection mechanism output, wherein the operationprocessing unit calculates a rotation angle Φ of the detectable rotationbody using the following equations (1) to (4), with assuming thecalculated rotation angle of the primary rotation body as θ1, an angleas θ2 of which the calculated rotation angle of the secondary rotationbody is multiplied by the predetermined rotation ratio, the convertedcycle of the signal of the primary rotation detection mechanism as T1, acycle as T2 (T1≠T2) of which the converted cycle of the signal of thesecondary rotation detection mechanism is multiplied by thepredetermined rotation ratio, an absolute value |T1−T2| as d for adifference between the cycle T1 and the T2; in a case where T1<T2, andθ2<θ1:Φ=θ1+T1(θ1−θ2)/d  (1); in a case where T1<T2, and θ2>θ1:Φ=θ1+T1(θ1−θ2)/d+T1T2/d  (2); in a case where T1>T2, and θ1≦θ2:Φ=θ1+T1(θ2−θ1)/d  (3); and in a case where T1>T2, and θ1>θ2:Φ=θ1+T1(θ2−θ1)/d+T1T2/d  (4).
 6. The rotation angle detector accordingto claim 5, wherein the m is one.
 7. The rotation angle detectoraccording to any one of claims 2, 4, 5, and 6, wherein the primaryrotation detection mechanism or the secondary rotation detectionmechanism comprises: a magnet to be attached to the primary rotationbody or to the secondary rotation body for generating a magnetic fieldof which intensity is varied continuously and periodically in a rotationdirection thereof; and two of magnetic detection elements to be arrangedfor having a predetermined angle around a center of rotation for theprimary rotation body or for the secondary rotation body in a vicinityof the magnet.
 8. The rotation angle detector according to claim 7,wherein the magnetic detection element is a Hall element.
 9. Therotation angle detector according to claim 7, wherein the magneticdetection element is a magnetoresistive element.